Government regulations strictly limit the transmit power of unlicensed transmitters so they do not interfere with licensed transmitters. Unfortunately, transmit power is dependent upon antenna impedance and efficiency which themselves vary when environmental changes occur. Furthermore, the quality of the transmitted signal is subject to change as a function of the number of unlicensed and licensed transmitters transmitting on the same frequency. As a result, the resulting transmit power occasionally drops below what regulations allow, and the range needlessly suffers as a consequence. It is therefore desirable to increase the transmitted power and thereby increase the quality of the transmitted signal under these, and perhaps other, conditions.
Modern transmitters for mobile terminals (e.g., phones) are particularly designed to use printed loop antennas or electrically small antennas. Unfortunately, the gains of these kinds of antennas tend to vary substantially from one transmitter to another and widely as a function of frequency. Further, the performance of both the antenna and the power amplifier in the transmitter has some temperature dependency.